The present invention generally relates to a semiconductor device having a smoothed edge of a layer and a method of producing the same.
Currently, a need exists for finer patterns for fabricating a semiconductor device. Anisotropic etching is suitable to forming finer patterns. For example, a polysilicon film is patterned by anisotropic etching in which an etching gas containing CC1.sub.4 /O.sub.2 is used. An edge of a side wall of the pattern thus formed is like a sheer cliff. In other words, an edge of the pattern rises sheer from an underlying layer. It is known that overhang portions are sometimes formed at side walls of patterns. As the height of the side wall of a lower layer increases, it becomes difficult to pattern an upper layer which covers the lower layer. It is known that most vertical side walls of layers are coated with spin on glass, or an etch-back process is employed, in order to eliminate the above-mentioned problem. However, such methods lead to an increased number of manufacturing steps. Particularly, it is very difficult to control the etch-back process.
In a dynamic random access memory device (hereinafter simply referred to as a DRAM), reduction in size of a projected area of a memory cell projected on a flat surface is desired. It is known that with a conventional stacked capacitor structure formed in the memory cell area equal to or less than 10 [.mu.m2.sup.2 ], it is very difficult to obtain a sufficient value of capacitance of a memory cell capacitor. In order to increase capacitance of the memory cell capacitor, it is conceivable to form a thicker storage electrode of polysilicon to thereby increase an area of a side surface of the storage electrode. With this structure, the entire surface area of memory cell capacitor can be prevented from decreasing. However, it is noted that patterning of a polysilicon film to obtain the storage electrode is greatly affected by a roughness of a surface of an underlying film under the polysilicon film. The polysilicon film used for forming the storage electrode is deposited on an interlayer insulation film which covers gate electrodes. Generally, the, surface of the interlayer insulation film has stepped portions, or convex and recessed portions due to the presence of the gate electrodes. The presence of great convex and recessed portions makes it difficult to pattern the polysilicon film deposited on the interlayer insulation film. As a result, a fine pattern of the storage capacitor cannot be obtained.